Re: [PATCH 2/4] arch/x86: implement the process_vm_exec syscall

[Andrei Vagin]

On Wed, Apr 14, 2021 at 07:09:15PM +0200, Oleg Nesterov wrote:
> On 04/13, Andrei Vagin wrote:
> >
> > +static void swap_mm(struct mm_struct *prev_mm, struct mm_struct *target_mm)
> > +{
> > +	struct task_struct *tsk = current;
> > +	struct mm_struct *active_mm;
> > +
> > +	task_lock(tsk);
> > +	/* Hold off tlb flush IPIs while switching mm's */
> > +	local_irq_disable();
> > +
> > +	sync_mm_rss(prev_mm);
> > +
> > +	vmacache_flush(tsk);
> > +
> > +	active_mm = tsk->active_mm;
> > +	if (active_mm != target_mm) {
> > +		mmgrab(target_mm);
> > +		tsk->active_mm = target_mm;
> > +	}
> > +	tsk->mm = target_mm;
> > +	switch_mm_irqs_off(active_mm, target_mm, tsk);
> > +	local_irq_enable();
> > +	task_unlock(tsk);
> > +#ifdef finish_arch_post_lock_switch
> > +	finish_arch_post_lock_switch();
> > +#endif
> > +
> > +	if (active_mm != target_mm)
> > +		mmdrop(active_mm);
> > +}
> 
> I think this should be unified with kthread_use_mm() somehow...

I agree.

> 
> And does it really need the "prev_mm" argument? It must be tsk->mm, no?

No, it doesn't. It is leftover of unuse_mm. BTW why do we pass mm to kthread_unuse_mm?

Thanks,
Andrei.